Want to see where the real power in your portfolio lies? Stop thinking of your investments as dollar amounts, and start looking at them as percentages of your total assets.

Eggs and baskets
My biggest holding by dollar value is Berkshire Hathaway, comprising between 10% and 20% of my portfolio.

To some people, that's way too much. A portfolio of between five and 10 stocks wouldn't give you much diversification, and some investors prefer to have no more than 5% of their money in a single stock. But in the case of Berkshire, I'm comfortable with the heavy weighting because of its management's integrity, and the company's broad diversification across disparate industries such as insurance, candy, furniture, and railroads.

Change happens
Even if you start with evenly weighted holdings, each will change in value over time. Winners will swell to represent a bigger piece of your pie. Should you sell some shares to rebalance your portfolio, or let the winners ride?

I face that dilemma with my Intuitive Surgical (Nasdaq: ISRG) shares. They've roughly tripled for me, and they now make up a sizeable chunk of my portfolio. I remain excited about the growth potential of robotic surgical equipment and this company's success in the industry. But since Intuitive has surpassed 5% of my portfolio, I need to watch it more closely and consider paring my position back a little, if my confidence wavers. The company's robust valuation is definitely one good reason to think about selling.

Small fries, big fries
The companies that take up the biggest percentages of your portfolio need to have your greatest confidence. Your biggest holdings have the most power to boost (or shrink) your portfolio, but small ones won't have much impact even when they're great picks.

Several years ago, Netflix's (Nasdaq: NFLX) performance and promise looked intriguing, despite fears that competitors Amazon.com (Nasdaq: AMZN) and Redbox parent Coinstar (Nasdaq: CSTR) could cause it some trouble. I invested a very small sum in the company, which has now increased in value eight-fold! But since it was such a small initial percentage of my portfolio, it's still not a major component, at about 2%. Tiny holdings can grow phenomenally, but it will be hard -- though not impossible -- for them to transform your portfolio.

It may seem silly to point out that your biggest holdings can help or hurt you the most, but we often forget to consider our holdings in terms of their weighting. If you keep an eye on your holdings' percentages, you'll know where they stand -- and what you should and shouldn't expect of them.

With acclaimed fast-growers apparently on sale, this could be the opportunity of the decade.

True to its name, The Motley Fool is made up of a motley assortment of writers and analysts, each with a unique perspective; sometimes we agree, sometimes we disagree, but we all believe in the power of learning from each other through our Foolish community.

Longtime Fool contributor Selena Maranjian owns shares of Akamai Technologies, Berkshire Hathaway, Netflix, and Intuitive Surgical. Berkshire Hathaway is a Motley Fool Inside Value recommendation. Akamai Technologies and Intuitive Surgical are Motley Fool Rule Breakers choices. Amazon.com, Berkshire Hathaway, and Netflix are Motley Fool Stock Advisor recommendations. The Fool owns shares of Berkshire Hathaway. Try any of our Foolish newsletter services free for 30 days. The Motley Fool has a disclosure policy.